Having detemined the structures of two forms of crystals of deoxy Hb S (Beta 6 glu-val) and of two forms of crystals of deoxy Hb C (Beta 6 glu-lys) at 3.0, 5.0, 4.0 and 4.5 angstroms respectively, it is proposed to go to 2.0 angstrom resolution and to refine these models so their calculated diffraction patterns best agree with those experimentally observed. After refinement the intermolecular contacts will be examined and catalogued. We have prepared crystals of deoxy Hb A, S, and C all in the same lattice and space group. It is proposed to determine the degree to which these crystals are isomorphous. The crystals of deoxy Hb C are resistant to X-ray damage, grow readily and diffract very well. It is proposed to work out their structure at 2.0 angstrom resolution. We have determined the crystal structure of deoxy Hb Vancouver (Beta 73 asp-tyr) at 5.0 angstrom resolution. It is proposed to go to 20 angstrom resolution and refine this structure.